1. Field of the Invention
The present invention pertains generally to devices, assemblies and systems for backflow prevention, and more particularly to a compact, light weight, low maintenance dual check valve backflow prevention apparatus of modular construction which provides low flow losses.
2. Description of the Background Art
Backflow prevention devices are widely used to prevent undesirable flow reversal under low flow, static or backpressure situations wherein clean upstream fluid sources can be contaminated by downstream fluid. Backflow prevention devices typically comprise one or two check valves, housed within a valve body, which undergo closure under backflow, backpressure or back siphonage conditions. The use of backflow prevention devices is generally required by law for cross-connected water supplies where potable water could undergo contamination due to flow reversal or back pressure conditions.
Currently used double check valve backflow preventers have proved deficient in various respects. Particularly, such back flow preventers are prone to relatively high flow losses due to the valve configurations and closure mechanisms employed, especially under low flow conditions. Further, back flow preventer assemblies typically require a bulky, heavy cast housing with a side port tube or extension and a separately cast port cover. This type of housing is expensive to manufacture and requires a substantial amount of space to accommodate the side port tube and cover. The check valves are typically bolted to seats within the housing, and can only be reached through the side port tube, which hinders access to the check valves. Maintenance and replacement of the check valves requires a person to reach through the side port tube and loosen bolts, compression rods or other internal hardware in order to remove the check valves, and thus tends to be a difficult and expensive operation. Still another drawback of presently used back flow preventers is that the check valves typically use complex, bulky, spring-biased closure mechanisms which require frequent maintenance and which can result in high flow losses due to friction.
Accordingly, there is a need for a backflow prevention apparatus which is compact and light weight, which is easy and inexpensive to manufacture, which does not have a side port tube, which provides easy access to internal check valves, which has check valves with simple, low-friction closure mechanisms, and which provides low flow losses. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in the background art.